Communication methods using a differential signal, for example, the RS485 standard, the RS422 standard, the LVDS (Low Voltage Differential Signaling) standard, and the like have been proposed as standards for high-speed serial transmission of digital signals.
FIG. 1A illustrates a circuit diagram of a conventional differential receiver, and FIGS. 1B and 1C illustrate examples for input-output characteristics of the differential receiver. Referring to FIG. 1A, a differential receiver 2r is configured to receive differential signals SIN+ and SIN− that are inputted to input terminals INP and INN, respectively, and generate an output signal SOUT based on a magnitude relationship between a amplitude of a difference ΔV (=SIN+−SIN−) and a predetermined threshold value VTH. Specifically, the differential receiver 2r is required to output a high level signal if ΔV>VH and a low level signal if ΔV<VL. Here, VH indicates a positive voltage and VL indicates a negative voltage. For example, these voltages are 200 mV and −200 mV, respectively.
The basic configuration and operation of the differential receiver 2r of FIG. 1A will be described below. The differential receiver 2r includes a comparator 10r. The comparator 10r outputs a high level signal if SIN+>SIN− and a low level signal if SIN+<SIN−. That is, the comparator 10 compares the amplitude of the difference ΔV (=SIN+−SIN−) with the threshold voltage VTH. In this case, if the threshold value VTH is fixed at 0V, chattering may occur due to noises. Thus, as shown in FIG. 1B, a hysteresis is set for the comparator 10r and the threshold voltage VTH switches between two values, i.e., VTHL and VTHH.
With the above configurations, a failure of short circuit may occur between wires of differential lines connected to the differential receiver 2r (which may be referred to as a short-circuit failure), and thus, it may be required to detect the failure in the differential receiver 2r. 
Thus, to detect the short-circuit failure, a method of offsetting the centers of the threshold voltages VTHL and VTHH as illustrated in FIG. 1C may be considered. In this method, the output of the comparator 10r can be fixed at a high level when a condition in which the differential wires are short-circuited to make SIN+ and SIN− equal to each other is maintained, thereby allowing the short-circuit failure to be detected.
Further, in the above configuration, a termination resistor (not shown) is generally inserted between the input terminals INP and INN. Accordingly, if a wire disconnection failure (e.g., an open failure) occurs or a transmission side is in an off state (e.g., a high impedance), the termination resistor causes the amplitude of the difference ΔV to become zero. As such, the differential receiver 2r of FIG. 1A can detect the open failure and the off state of the transmission circuit.
However, if an offset is introduced for the short-circuit failure as shown in FIG. 1C, it is necessary to reduce a hysteresis width as compared to that in FIG. 1B, which may result in lower noise resistance.